Replace the infinitives by the Past Indefinite, the Present Perfect or the Present Perfect Continuous.

1.At last you (to open) the door. I (to ring) for an hour at least, I think. 2. Here you are at last. I (to wait) for you for ten minutes. 3. The workers (to work) hard since Tuesday. 4. The scientists (to carry out) a lot of experiments before they (to get) positive results. 5. It (not to rain) for a long time. 6. He (to work) at this project for a long time and(not to finish) it yet. 7. How long you (to know) her? I (to know) her for three years. 8. Last night my friends and I (to decide) to stay in town for I lie summer. 9. They (to discover) diamonds in South Africa in the 19th century. 10. The concept of the atom (not to exist) before 1804.

1.At last you  have opened the door. I have been  ringing  for an hour at least, I think. 2. Here you are at last. I have been  waiting  for you for ten minutes. 3. The workers have been  working  hard since Tuesday. 4. The scientists have carried out a lot of experiments before they get positive results. 5. It  has been  raining  for a long time. 6. He has been  working at this project for a long time and has not finished it yet. 7. How long have you been   knowing her? I have been knowing her for three years. 8. Last night my friends and I  decided to stay in town for I lie summer. 9. They  discovered diamonds in South Africa in the 19th century. 10. The concept of the atom has not to existed before 1804.